The hydroformylation reaction is employed on a commercial scale to prepare straight chain and branched chain mixtures of aldehydes and alcohols from olefinically unsaturated hydrocarbons.
The selective production of straight chain aldehydes and alcohols is particularly desirable. Higher oxo alcohols have become important intermediates for synthesis of biodegradable surface-active agents, lubricant esters, and plasticizers. In each of these products straight chain alcohol derivatives are preferred because of biodegradability and other advantageous properties. There is continuing development effort to increase alpha-olefin hydroformylation selectivity to linear paraffinic aldehydes and alcohols.
Cobalt carbonyl is a conventional catalyst employed for hydroformylation reaction, but large quantities of branched chain aldehydes are produced with this catalyst. Rhodium carbonyl complexes containing tertiary phosphine or phosphite ligands [Evans et al, J. Chem. Soc. A, 3133 (1968); Pruett and Smith, J. Org. Chem., 34, 327 (1969)] are useful at low pressures and give higher ratios of straight chain to branched chain products. Similar cobalt carbonyl complexes [Slaugh and Mullineaux, J. Organometal. Chem., 13, 469 (1968)] also give more straight chain product, but produce alcohols as the primary products.
More recently developed hydroformylation catalysts and processes achieve some selectivity to linear products but still result in a high yield of branched chain aldehyde and alcohol products. Illustrative of recent advances in hydroformylation technology are U.S. Pat. Nos. 3,480,659; 3,488,296; 3,515,757; 3,652,676; 3,681,465; 3,876,672; 3,933,919; 3,939,188; 3,956,177; 3,965,192; 3,981,925; and 3,984,486.
U.S. Pat. No. 3,939,188 describes a hydroformylation process in which propylene is converted to aldehydes in a normal/iso ratio of 2:1 in the presence of a zero valence rhodium catalyst which is stabilized by selected monodentate, bidentate, tridentate or quadradentate ligands: EQU (Ph.sub.3 P).sub.3 Rh--Rh(PPh.sub.3).sub.3
U.S. Pat. No. 3,956,177 describes the preparation of a hydroformylation catalyst involving admixture of an alicyclorhodium halide, a reducing agent such as hydrazine, and a phosphorus-containing ligand. In EXAMPLE 1 of the patent reference, hexene-1 is converted to 77.5 percent n-heptaldehyde, 5.6 percent branched C.sub.7 -aldehydes, and 16.9 percent of internal hexenes.
U.S. Pat. No. 3,965,192 discloses a process for hydroformylation of olefins with a tris(triphenylphosphine) rhodium carbonyl hydride type of catalyst. In EXAMPLE 1 of the patent reference, propylene is converted to aldehydes in a normal/iso ratio of 2:1.
U.S. Pat. No. 3,981,925 discloses a process for hydroformylation of olefins to aldehydes in the presence of a ligand stabilized platinum halide complex in combination with a Group IVA metal halide. The hydroformylation selectivity of the U.S. Pat. No. 3,981,925 process favors formation of straight chain aldehyde, e.g., in Example 1 the mole ratio of 1-octylaldehyde to 2-methylheptaldehyde product from heptene-1 hydroformylation is 9:1. Also produced are 2.7 mole percent of heptene-2 and heptene-3 isomerization products.
There remains further need for improved hydroformylation efficiency and selectivity to straight chain derivatives, and a concomitant reduction in the yield of isomerization, hydrogenation and polymerization products.
Accordingly, it is a main object of the present invention to provide a hydroformylation process for converting alpha-olefins to aldehydes in a normal/iso mole ratio of at least 5:1 and in a conversion efficiency to aldehydes of at least 95 mole percent.
It is a further object of this invention to provide a novel rhodium catalyst system for hydroformylation of alpha-olefins which has improved efficiency and selectivity for linear aldehyde formation.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.